Fluid transport systems are well known and used in a number of applications. One specific application of transporting a fluid in a machine is the transportation of ink in a printer. Common examples of inks include aqueous inks and phase change or solid inks. Aqueous inks remain in a liquid form when stored prior to being used in imaging operations. Solid ink or phase change inks typically have a solid form, either as pellets or blocks of colored ink, which are inserted into feed channels in a printer through openings to the channels. After the ink sticks are fed into the printer, they are urged by gravity or a mechanical actuator to a heater assembly of the printer. The heater assembly includes a heater and a heat transfer surface. The heater, which converts electrical energy into heat, is positioned proximate the heat transfer surface to heat the surface to a temperature that melts an ink stick coming into contact with the surface. The heat transfer surface can be oriented to drip melted ink into a reservoir and the ink stored in the reservoir continues to be heated while awaiting subsequent use.
Fluid couplings in the printer supply the liquid ink held in each reservoir of colored ink to an inkjet printing apparatus. Either a pump or the force of gravity is used to move the ink from the reservoir to a manifold in the inkjet printing apparatus. As the inkjets in the inkjet printing apparatus eject ink onto a receiving medium or imaging member, the action of the diaphragms in the inkjet ejectors pull ink from the manifold. Various embodiments of inkjets include piezoelectric and thermal devices that are selectively activated by a controller with an electrical firing signal.
Phase change ink printers often include one or more heaters that maintain a supply of phase change ink in a liquid state for use during printing operations. Some of the heaters maintain a small supply of ink in the liquid state within the reservoir and other fluid conduits within the printheads. Typically, the heaters are electrical heaters that consume electrical energy to maintain the phase change ink in a liquid phase. In order to reduce energy usage, phase change ink printers deactivate various components, including heaters, in the printer during a sleep mode to conserve energy. The ink held in the inkjet printing apparatus and inkjets cools and solidifies in some sleep modes.
While sleep modes enable a printer to operate with reduced electrical energy consumption, the solidification of phase change ink within the printer presents difficulties to printing high quality documents when the printer emerges from sleep mode. As phase change ink within the inkjet printing apparatus cools and solidifies, the ink contracts and air enters the pressure chambers and fluid conduits within the inkjet printing apparatus. As the solidified ink heats and liquefies, the air forms bubbles in the liquefied ink that can prevent inkjets in the inkjet printing apparatus from operating reliably. Additionally, liquid ink that is in the chambers within a single jet can form a meniscus across the nozzle of the inkjet whereby surface tension of the ink across the nozzle retains the ink within the pressure chamber before the inkjet ejects an ink drop. The meniscus breaks as the solid ink liquefies, resulting in some ink flowing through the nozzle, also referred to as “drooling” ink. The drooled ink can contaminate other nozzles in the printhead or separate from the printhead and produce errant marks on the image receiving member.
To eliminate air bubbles and restore the meniscus between liquefied ink and the nozzle of each inkjet, the inkjet printing apparatus undergoes a “purge” operation where pressure applied to the inkjet printing apparatus urges the liquid ink and the air bubbles through the nozzles of the inkjets. In a typical purge operation, the inkjets emit a stream of ink that flows down a face of the inkjet printing apparatus and is collected in a waste ink receptacle instead of being ejected as individual ink drops. The remaining ink on the face of the head is subsequently wiped with a silicone wiper blade. The purge operation removes air bubbles from the inkjet printing apparatus and establishes a meniscus between the liquid ink and the inkjet nozzles to enable reliable operation of the inkjets.
In existing printers, the purged ink is typically collected in a waste reservoir and is eventually discarded. In printers that enter sleep modes more often to reduce electrical energy consumption, the number of purge cycles and the corresponding amount of discarded ink increases. Thus, improvements to phase change ink printers that reduce or eliminate discarded ink produced during purge cycles are desirable.